EFFECT OF AIR SUPPLEMENT ON THE PERFORMANCE OF CONTINUOUS ETHANOL FERMENTATION SYSTEM

For the purpose of improving ethanol productivity, the effect of air supplement on the performance of continuous ethanol fermentation system was studied. The effect of O2 supplement on yeast concentration, cell yield, cell viability, extracellular ethanol concentration, ethanol yield, maintenance coefficient, specific rates of glucose assimilation, ethanol production and ethanol productivity were evaluated,using a high alcohol tolerant Saccharomyces cerevisiae STV89 strain and employing a continuous fermentor equipped with an accurate air metering system in the flow rate range 0-11 ml air/l per h. When a small amount of O2 up to .apprx. 80 .mu. mol O2/l per h was supplied, the ethanol productivity was significantly enhanced as compared to the productivity of the culture without any air supplement. The O2 supplement improved cell viability considerably and the ethanol tolerance level of yeast. As the air supply rate was increased, from 0-11 ml air/l per h while maintaining a constant dilution rate at .apprx. 0.06 h-1, the cell concentration increased from 2.3 to 8.2 g/l and the ethanol productivity increased from 1.7 to 4.1 g ethanol/l per h, although the specific ethanol production rate decreased slightly from 0.75 to 0.5 g ethanol/g cells per h. The ethanol yield was slightly improved also with an increase in air supply rate, from .apprx. 0.37 to 0.45 ethanol/g glucose. The maintenance coefficient increased by only a small amount with the air supplement. This kind of air supplement technique may very well prove to be of practical importance to a development of a highly productive ethanol fermentation process system, especially as a combined system with a high density cell culture technique.